Terminal-Centric Location Services for the IP Multimedia Subsystem

Location-based services in 3G and beyond networks depend on high-accuracy location data. Today's 2G and 3G access networks determine user location in a network-centric manner. The accuracy of these location mechanisms depends on the radio infrastructure near the user's geographical position and is typically limited to hundreds or thousands of meters. This precision is inadequate for typical location-based services like city maps or route planners. In this paper we present a terminal-centric location enabler that integrates seamless with the existing IP multimedia subsystem presence architecture and interoperates with network-centric location mechanisms. We argue that the user terminal itself, equipped with location sources like GPS receivers, can determine the geographical position with an optimum of accuracy. In consequence, the user terminal should be used as the primary source for location information. We extend the existing and well-known concept of presence by defining location as a type of presence information that is of interest to users. Terminal-based triggers and filters reduce the amount of traffic on the air interface and enable a scalable location architecture. We present the implementation of a J2ME-based mobile terminal prototype, which uses GPS as location source and interfaces with IMS location services